The issue began about 10:30 a.m. PST and affected a subset of users of both the Web page-based Gmail Chat and the installed Google Talk software, spokesman Andrew Kovacs said. Because of the problem, sometimes when people sent a message they'd get an error message it wasn't sent and the recipient didn't receive it, but often resending the message worked, he said.

"This issue has been resolved for most users, and we expect a resolution for all users within the next couple of hours," Kovacs said about three hours after the problem began.

Google's core business is in search and advertising, but it's trying to expand to be a fuller-featured Internet destination with Gmail, Google Calendar, and Google Docs, which collectively are offered to paying customers as Google Apps subscriptions. Google offers a service level agreement to those customers.